How can I make a custom IK arm rig on an already made Auto Rig Pro rig
I guess you already found your answer but maybe other peoples will need this too.
Here is one way to do :
Once you have your rig, go into pose mode and select the rectangle part of the hand.
Then on the panel on the upper right of the screen go to &quot;tool&quot;

Under Rig Main Properties you have &quot;IK-FK Switch&quot;. 1 = FK ; 0 = IK
So if you want IK, switch it to O. I hope this will help.